a) Field of the Invention
This invention relates to an improvement in a brake band employed in a power transmission for an automotive vehicle or the like.
b) Description of the Related Art
In a power transmission for an automotive vehicle or the like, it is generally practiced as a common technique to pull a brake band tight against a clutch drum to apply braking force to the clutch drum. Lubrication of a lining of the brake band is effected by oil guided out through oil apertures formed in the clutch drum or by oil caused to spout out to and around the lining.
In view of the public concern about energy and environment, a brake is now required to be small and light, to produce a smaller shock when actuated, and to have a high torque capacity. Keeping step with the recent trend toward automotive engines of higher rpm and higher power output, the brake must also successfully meet the current tendency toward severer use conditions where the brake must withstand high energy. The demand for a brake band is therefore becoming increasingly severer.
As far as oil is concerned, it is desired to achieve sufficient lubrication and seizure prevention by a small amount of oil leaked out while having lubricating other parts. Where no apertures are formed, for example, in a clutch drum as a braked member, only a small fraction of oil, which has been caused to spout out under centrifugal force subsequent to lubrication of a clutch mechanism accommodated within the clutch drum, is used as a lubricant for the brake band. To meet the above-described trend toward automotive engines of higher rpm and higher power output, oil supplied in a small amount from opposite side edges of the lining is too little to achieve sufficient lubrication, leading to the problem that the lining may burn up.
FIG. 6 is a transverse cross-sectional view of an illustrative conventional brake band combined with a clutch drum, whereas FIG. 7 is a plan view of the brake band, namely, a combined unit of a lining and strap as viewed in a direction from an inner side of the lining. Designated generally at numeral 10 in FIG. 6 is a clutch mechanism. Incidentally, this clutch mechanism is of the common art and its detailed description is therefore omitted herein.
A clutch drum 11 as a braked member is provided on an outer peripheral wall thereof with a brake band 50. The brake band 50 is composed of a lining 20 and a strap 30 arranged on an outer side of the lining 20. The lining 20 is arranged for contact with the outer peripheral wall of the clutch drum 11 and, in the example illustrated in the drawings, centrally defines grooves 22. The strap 30 is employed to pull the lining 20 tight against the outer peripheral wall of the clutch drum 11.
Where the clutch drum 11 is not provided with any oil apertures, oil which has lubricated the clutch mechanism 10 is caused to spout out under centrifugal force through a fitted area 12 between the clutch drum 11 and an associated component as indicated by arrow R. It is however only a small fraction of the oil that is used for the lubrication of the brake band 50.
As is depicted in FIG. 7, when the combined unit of the lining 20 and the strap 30 is observed from the inner side of the lining 20, oil apertures 34 formed through the strap 30 are located opposite respective oil grooves 21 formed through the lining 20. A portion of oil, which has been caused to spout out under centrifugal force through the fitted area 12 as described above, enters the oil grooves 21 through the oil apertures 34 in the strap 30 so that the lining 20 is lubricated. The amount of the oil actually used for the lubrication is however still small. The oil, which is supplied in the small amount through the oil apertures 34 in the strap 30 and from the opposite side edges of the lining 20, cannot provide sufficient lubrication, thereby unavoidably resulting in the inconvenience that the lining may be burnt up.
Incidentally, a hole 35 shown in FIG. 7 is a rivet hole through which a rivet is allowed to extends to unite the lining 20 and the strap 30 together.